The main constituents of pearl are

(A) Calcium carbonate and magnesium carbonate

(B) Aragonite and conchiolin

(C) Ammonium sulfate and sodium carbonate

(D) Calcium Oxide and ammonium chloride 

 If safe storage is to be ensured, the moisture content of foodgrains at the time of harvesting should not be higher than:

(A) 14%

(B) 16%

(C) 18%

(D) 20%

The half-life of a radioactive element is $5$ years. The fraction of the radioactive substance that remains after $20$ years is:

(A) $\frac{1}{2}$

(B) $\frac{1}{4}$

(C) $\frac{1}{8}$

(D) $\frac{1}{16}$

Below are two statements, one labeled as Assertion(A) and the other as Reason (R).

Assertion (A): A lock of Einstein's hair, if scientists could locate it and extract its DNA, could help produce another Einstein by cloning.
Reason (R): The DNA extracted from the cell of an embryo at an early stage of development can be transferred to individual eggs, which can be implanted into the uterus of a surrogate mother to give birth to an identical offspring.

In the context of the above two statements, which one of the following is correct?

Which one of the following vitamins is considered to be a hormone?

(A) Vitamin A

(B) Vitamin B

(C) Vitamin C

(D) Vitamin D

Galvanised iron sheets are protected from rusting due to the presence of a layer of--

(A) Lead

(B) Chromium

(C) Zinc

(D) Tin

In recent years there has been some concern over the threat posed by the Mathura Oil Refinery and the Thermal Power Plants to the Taj Mahal in Agra. The scientific basis of any possible damage to the Taj is mainly